1. Field of the Invention
This invention relates to low cost steel gas generator or inflator assemblies that utilize the combustion of a solid fuel gas generant composition for the generation of a gas for rapidly inflating vehicle passive restraint inflatable crash protection bags, and more particularly, to a device comprising an improved ignition train for such low cost steel inflator assemblies, but having application to any inflator the construction of which is modifiable to allow for the utilization of such a device.
2. Description of the Related Art
Inflators for the inflation of inflatable crash protection or "air bag" restraint systems must be constructed to withstand the mechanical and thermal stresses that are generated by such systems. This has led to the use for lighter weight systems of aluminum instead of steel in constructing the inflator housing and other structural components. A form of light weight inflator that utilizes aluminum for the housing structure is disclosed in U.S. Pat. No. 5,419,578 that was granted to Kirk Storey, Michael P. Jordan and Brent Olsen and to the assignee of the present invention.
The aluminum housing constructions of such prior art inflators include first and second structural components, a diffuser and a base. The diffuser and base are welded together in a single inertia welding operation to form igniter, combustion and filtering chambers, the assembly being welded in a wholly loaded condition.
Some of the internal components of the inflators known in the prior art are capable of being adversely influenced by environmental factors. As a result, a problem is encountered when the welds used to secure the diffuser and base components together are not airtight or hermetic, that is, the welds allow air to escape or enter the inflator.
In the aforementioned U.S. patent there is disclosed a welded inflator housing construction comprising diffuser and base components made from different aluminum alloy materials. These different aluminum alloy materials provide an inflator housing construction having an improved hermetic seal, i.e., improved leak rate performance. A disadvantage of this construction is that it is expensive to manufacture.
In all of the embodiments of an inflator having a low cost steel housing construction, there is a requirement for the ignition train to be installed last. Along with this requirement is the need to seal the gas generant composition, and the ignition train, also, from the environment. This is because, similarly to inflator housing constructions made from aluminum, exposure to the environment has been shown to degrade or prevent the proper operation of the inflator. It is very difficult to combine these requirements as the processes needed involve the use of high energies to seal or close the ignition train into the main body, that is the gas generating combustion chamber, of the inflator. These energies potentially can ignite the inflator during construction.
Other alternative embodiments involve elaborate seals or fastening mechanisms which would be difficult to assemble and relatively expensive to manufacture.
Thus, there is a need for further improvement in the structure of inflators having a low cost steel housing construction to overcome this problem involving the requirement regarding installation last of the ignition train and hermetic sealing. It is to a practicable, low cost solution of this problem that the present invention is directed.